Typical offset lithographic printing presses comprise five basic components: a web feed, a printing unit or units, a dryer, a chill roll unit and a folder. The printing press has one or more printing units depending upon the number of colors which are needed for the particular printing task. A separate printing unit is needed for each color. A typical newspaper press only has one printing unit for the color black. A full color printing press may have either four or five printing units depending upon whether or not a special color is used. The three primary printing colors are yellow, cyan and magenta.
Each printing unit comprises a plate cylinder having a printing plate mounted on its outer circumferential surface, a blanket cylinder having a printing blanket mounted on its outer circumferential surface, an inking system and a dampening system. The inking system includes a plurality of rollers which transfer ink from an ink reservoir to the surface of the printing plate. The dampening system also includes a plurality of rollers which transfer dampening solution from a dampening reservoir to the surface of the printing plate. The dampening solution is provided to facilitate the transfer of the ink from the printing plate onto the surface to be printed, which is typically paper. The plate cylinder rotates in contact with the blanket cylinder. The image from the printing plate is therefore transferred from the surface of the printing plate to the surface of the printing blanket which in turn transfers the image to the paper. This type of printing, known as offset printing, is an indirect printing process because the printed image is first transferred to a printing blanket before it is printed on the paper. In direct printing processes, such as in most intaglio and flexographic printing techniques, the printed image is transferred directly from the printing plate to the paper.
A web feed feeds paper through each of the printing units in an offset lithographic printing press. The paper is fed in a web form, i.e., one continuous sheet. A web is usually anywhere between 18.0 inches and 80.0 inches wide. Typically, up to eight pages can be printed across the width of the web. The web passes between a pair of impression cylinders as it passes through each printing unit. At least one of the pair of impression cylinders is a blanket cylinder. To achieve double-sided printing, both of the impression cylinders are blanket cylinders, i.e., one blanket cylinder is mounted on one side of the web and the other is mounted on the other side of the web. Each blanket cylinder has a corresponding plate cylinder and inking and dampening system. Thus, a printing unit which can print on both sides of the web has two printing sections. Different images can therefore be printed on the opposite sides of the web. The diameters of the blanket cylinders may be the same size as the plate cylinders, or they may be some multiple thereof, i.e., 2 or 3 times the size.
Each plate cylinder and blanket cylinder, generically referred to as a printing cylinder, is mounted between two side flames of the printing unit. Each side frame has a pair of cylindrical bores into which the shafts of the adjacent cylinders fit. A cylindrical bearing housing sleeve is provided which is disposed between the shaft of each cylinder and the corresponding cylindrical bore in the frame. Anti-friction bearings are also provided between the cylindrical bearing housing sleeve and the shaft of the cylinder. The print quality, in part, depends on how well the bearing housing sleeves fit into the cylindrical bores in the frame. Typically, the closer the fit, the better the print quality. However, the fit must also be free to a certain extent to allow for thermal expansion of the bearing housing sleeves as they heat up during operation of the printing press. The fit must also be free to a certain extent to provide a rotational clearance so that adjacent printing cylinders can be moved into or out of contact with ("thrown-off") one another. It is often necessary to "throw-off" the printing cylinders so that the surfaces of the cylinders can be cleaned or the printing plate or printing blanket can be changed. The printing cylinders are typically not separated from one another more than between 0.0625 to 0.125 inches when they are in the "thrown-off" position.
A drawback with prior art bearing housing sleeves is that their fit within the corresponding frame bores cannot be adjusted to obtain a close fit. Excessive "play" exists to allow for thermal expansion of the bearing housing sleeves so that they do not get stuck in the frame bores and thus prevent the printing cylinders from being moved out of contact with one another for servicing. As a result of this excessive "play," print quality suffers.
One solution has been to place a tapered anti-friction bearing in the space between the bearing housing sleeve and the frame bore. By axially adjusting the position of the tapered anti-friction bearing, the "fit" between the bearing housing sleeve and the frame bore can be adjusted. During operation, the tapered anti-friction bearing can be adjusted so that a close fit between the bearing housing sleeve and the frame bore can be obtained. By achieving a close fit between the bearing housing sleeve and the frame bore, a constant pressure can be maintained between the printing cylinders which is an important operating condition necessary for obtaining a high quality printed image. The tapered bearing may also be adjusted to loosen the "fit" between the bearing housing sleeve and the frame bore so that the printing cylinders can be thrown-off from one another. This is typically achieved by rotating bearing housing sleeves of at least one of the printing cylinders which are eccentric. As eccentric bearing housing sleeves are rotated, the cylinder mounted in these eccentric bearing housing sleeves moves laterally away from the adjacent printing cylinder. A drawback of this solution, however, is that use of the tapered bearings takes more space, makes for a more complicated design, and requires additional parts and thus increases the cost of manufacturing the printing press.
The present invention is directed to overcoming, or at least minimizing, some of these problems.